Update README.md (#515)
Update README.md (#515)


webcomponents/webcomponents.org,andymutton/beta,andymutton/beta,webcomponents/webcomponents.org,customelements/v2,andymutton/beta,andymutton/beta,andymutton/v2,andymutton/v2,andymutton/v2,customelements/v2,andymutton/v2,customelements/v2,customelements/v2,webcomponents/webcomponents.org